Numerous types of roof assemblies have previously been proposed for pre-engineered buildings in efforts to provide a watertight roof assembly, while at the same time enabling the roof assembly to expand and contract as changes in temperature are encountered. Typical of such prior art roof assemblies of considerable success in recent years is the standing seam roof assembly. The panel members of the standing seam roof assembly are joined along lapped together side edges forming the standing seams. The panel members of the standing seam roof are secured to the secondary structural members by either clips or through fasteners. Clips can be of two types: floating (one or two piece moveable); or fixed (one piece with no movement allowed between the panel and its supporting structure). Through fasteners attach the panels to underlying support structure and substantially fix or lock the panels and support structure together so that no differential movement can occur.
Roofs may be classified as shed roofs and low slope gasket roofs. Shed roofs are roofs that shed water because gravity pulls the water down and away from panel joints more effectively than wind or capillary action propel water thought the joint. Shed roofs generally occur over slopes of three to twelve or greater. Low slope gasket roofs, on the other hand, provide roof joints that are made watertight by placing a gasket material between the panel joints and securing the gasket in place by, for example, encapsulating the gasket material or exerting pressure upon it. Generally, low slope gasket roofs are usually 1/4 to twelve slope or greater.
Heretofore, field seamed gasket joints used on large roofs have generally been limited to using two-piece clips wherein movement between the roof and its underlying structure took place within the clip. The reason for this is that in the past the line of sealant serving as a gasket and the top hook portion of the clip intersected and if the clip hook moved in relation to the panel which held the sealant, the relative movement deformed and destroyed the gasket seal. One-piece clips have been used freely in small and shed roofs where a gasket seal was not required.
Standing seam metal roofs exhibit considerable diaphragm strength and it is desirable to use this strength by interconnecting the roof to its support frame to help stabilize the support frame, rather than to brace and stabilize the support frame by other means.
Past practices have been to stabilize the support frame by means of separate bracing and on gasket roofs to use a suitable two-piece floating (moveable) clip to allow the brace and frame to remain fixed and for the panel to move in relation to the frame as it is subjected to temperature change or other forces, or to limit the length of the panel run to about 40 feet so that the movement of the panel as it expands and contracts is low and does not materially damage its connection to the underlying structure.
However, the desirable result of eliminating detrimental differential movement between the panel and its support structure on large roofs may also be achieved by construction of the underlying support so that it moves slightly to accommodate the movement of the roof as it is being subjected to movement because of temperature change or other forces. This means of construction is exemplified in a system produced bye ReRoof America, Inc., referred to as the Flex Frame support system.
The interconnection of the panel members of the standing seam roof lend stiffness and strength to a flexible roof structure while allowing the roof structure to expand and contract as a function of the coefficient of expansion of the panel material and the temperature cycles of the roof panels.
If one of the means of using floating clips or of using a fixed connection between the panel and the flexible framing is not used, the repeated action of expansion and contraction of the panel member tends to weaken the panel-to-panel lap joints and the panel to framing connection, causing panel separation, structural failure and roof leakage. Leaks are generally caused by the weakening of the fastening members and working or kneading of the sealant disposed at the joints. Prior art sealant for such roof assemblies requires adhesion, flexibility and water repellence. Further, in many instances the pressure on the sealant varied greatly throughout the length of the sidelap and end lap joints of the panels, resulting in uneven distribution and voids in the joint sealant.
Many of the problems discussed hereinabove encountered in prior art standing seam roofs, such as structural failures and leaks, have been overcome by a standing seam floating roof assembly such as is disclosed in U.S. Pat. No. 5,737,894 issues to Harold G. Simpson. The standing seam floating roof assembly is formed of elongated metal panels, each of which is provided with a female member formed along one longitudinal edge and a male member formed along the opposed longitudinal edge, adjacently disposed panels being joined by interlocking female and male members thereof to form the standing seam joint. Clips interconnect the standing seam joints and the underlying secondary structure, with the upper portions of the clips hooking over the male members of the panels. Most such clips are of the sliding type which permits the hooking portion to move relative to a supporting base portion connected to the secondary structure, while relative motion between the clip hook and the metal panel is substantially prevented. A sealant material is disposed to form a moisture dam in the interlocking joint of the female and male members.
In addition to the use of standing seam roof assemblies on newly constructed pre-engineered buildings., standing seam roof assemblies are also finding increased usage in another segment of the roofing industry, that of "built-up roof" replacement. Generally, a built-up roof is formed of a plurality of sections which are interconnected and overcoated with asphaltic composition to provide a watertight seal. While such substantially horizontal roof assemblies have generally served successfully, problems have nevertheless been encountered as the built-up roof ages, when the building settles, or when construction errors result in water standing in pockets on the roof assembly. This standing water often results in deterioration of the roof, causing leaks and other problems.
A need has long been recognized for a means of replacing a built-up roof, as well as other conventional roofs, which does not require substantial modification to the preexisting roof and which is economical both in fabrication and on-site construction. Further, it is highly desirable that the new roof assembly be capable of providing a new roof surface independent of the variations in the surface of the preexisting roof. Past repair methods, especially those capable of altering the slope of the roof surface to improve drainage characteristics, have required substantial destruction of the original roof and extensive custom construction, thus exposing the building and its contents to damage by the elements during the reroofing process and being excessively time consuming.